U.S. patent application number 14/932110 was filed with the patent office on 2016-05-19 for fuel cell system and control method of fuel cell system.
This patent application is currently assigned to TOYOTA JIDOSHA KABUSHIKI KAISHA. The applicant listed for this patent is TOYOTA JIDOSHA KABUSHIKI KAISHA. Invention is credited to Yoshiaki NAGANUMA, Tomohiro OGAWA.
Application Number | 20160141676 14/932110 |
Document ID | / |
Family ID | 55855674 |
Filed Date | 2016-05-19 |
United States Patent
Application |
20160141676 |
Kind Code |
A1 |
OGAWA; Tomohiro ; et
al. |
May 19, 2016 |
FUEL CELL SYSTEM AND CONTROL METHOD OF FUEL CELL SYSTEM
Abstract
An object is to provide a technique that a current state of a
fuel cell may be detected more accurately. A fuel cell system
includes a controller, a fuel cell, and an impedance measurer that
may measure an impedance of the fuel cell. The controller obtains a
first impedance value that expresses the impedance of the fuel cell
in a predetermined state, acquires a second impedance value that
expresses the impedance of the fuel cell that is measured by the
impedance measurer during operation control of the fuel cell, and
performs operation control of the fuel cell using the first
impedance value and the second impedance value.
Inventors: |
OGAWA; Tomohiro;
(Miyoshi-shi, JP) ; NAGANUMA; Yoshiaki;
(Toyota-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TOYOTA JIDOSHA KABUSHIKI KAISHA |
Toyota-shi |
|
JP |
|
|
Assignee: |
TOYOTA JIDOSHA KABUSHIKI
KAISHA
Toyota-shi
JP
|
Family ID: |
55855674 |
Appl. No.: |
14/932110 |
Filed: |
November 4, 2015 |
Current U.S.
Class: |
429/430 |
Current CPC
Class: |
G01R 31/389 20190101;
Y02T 90/40 20130101; H01M 8/04992 20130101; H01M 2008/1095
20130101; H01M 8/04641 20130101; H01M 8/04753 20130101; Y02E 60/50
20130101; H01M 2250/20 20130101; H01M 8/04365 20130101 |
International
Class: |
H01M 8/04 20060101
H01M008/04 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 13, 2014 |
JP |
2014-230864 |
Claims
1. A fuel cell system, comprising: a fuel cell; an impedance
measurer that measures an impedance of the fuel cell; and a
controller for performing an operation control of the fuel cell,
wherein the controller obtains a first impedance value that
expresses the impedance of the fuel cell in a predetermined state,
acquires a second impedance value that expresses the impedance of
the fuel cell that is measured by the impedance measurer during the
operation control of the fuel cell, and performs operation control
of the fuel cell using the first impedance value and the second
impedance value.
2. The fuel cell system according to claim 1, wherein the
controller corrects the second impedance value by using the first
impedance value, and performs the operation control of the fuel
cell on the basis of the second impedance value after
correction.
3. The fuel cell system according to claim 1, further comprising: a
storage portion for storing the first impedance value, wherein the
controller executes an update process that updates the first
impedance value stored in the storage portion when the fuel cell
reaches the predetermined state during the operation control of the
fuel cell, the controller, in the update process, reacts the first
impedance from the storage portion as an original value, obtains
the impedance of the fuel cell by the impedance measurer as a
present value, calculates an updated first impedance value by using
the original value and the present value, and stores the updated
first impedance value in the storage portion as the first impedance
value.
4. The fuel cell system according to claim 3, further comprising: a
temperature detect portion that detects an operating temperature of
the fuel cell, wherein the controller determines that the fuel cell
reaches the predetermined state when the operating temperature of
the fuel cell is within a predetermined temperature range, and
executes the update process.
5. The fuel cell system according to claim 4, wherein the
controller determines that the fuel cell reaches the predetermined
state when the operating temperature of the fuel cell is within the
predetermined temperature range during a predetermined time period,
and executes the update process.
6. The fuel cell system according to claim 3, wherein the
controller updates the first impedance value with reflecting a
difference between the present value and the original value so that
a difference between the present value and the updated first
impedance value is reduced.
7. The fuel cell system according to claim 6, wherein the
controller updates the first impedance value by using a correction
strength that express a extent of reflection of the difference
between the present value and the original value in the update
process.
8. The fuel cell system according to claim 7, further comprising:
an initialization detector for detecting a history of
initialization of the storage portion, wherein the controller
changes the correction strength so that the extent of reflection of
the difference between the present value and the original value
becomes large when the history of initialization of the storage
portion is detected by the initialization detector.
9. The fuel cell system according to claim 6, wherein the storage
portion is a first storage portion, and the fuel cell system
further comprises a second storage portion for storing an initial
value of the first impedance value; and an initialization detector
for detecting a history of initialization of the first storage
portion, wherein the controller sets a value that is larger than
the initial value of the first impedance value stored in the second
storage portion as the original value, and restarts the update of
the first impedance value in the update process, when a history of
initialization of the first storage portion is detected by the
initialization detector.
10. The fuel cell system according to claims 1, further comprising:
a reaction gas supply portion for supplying reaction gas to the
fuel cell, wherein the controller controls the reaction gas supply
portion in the operation control of the fuel cell using the first
impedance value and the second impedance value.
11. A control method of a fuel cell system, comprising: a first
impedance acquisition process of obtaining a first impedance value
that expresses an impedance of a fuel cell in a predetermined
state; a second impedance acquisition process of acquiring a second
impedance value that expresses the impedance of the fuel cell and
is obtained by measuring the impedance of the fuel cell during an
operation control of the fuel cell; and a control process of
executing the operation control of the fuel cell by using the first
impedance value and the second impedance value.
12. The control method according to claim. 11, further comprising:
a correct process of correcting the second impedance value by using
the first impedance value, wherein the control process executes the
operation control of the fuel cell on the basis of the second
impedance value after correction.
13. The control method according to claim 11, further comprising:
an update process of updating the first impedance value, which is
stored in a storage portion when the fuel cell reaches the
predetermined state during the operation control of the fuel cell,
wherein the update process includes reading the first impedance
value from the storage portion as an original value, obtaining the
impedance of the fuel cell by measuring the fuel cell as a present
value, calculating an updated first impedance value by using the
original value and the present value, and storing the updated first
impedance value in the storage portion as the first impedance
value.
14. The control method according to claim 13, further comprising: a
temperature detect process of detecting an operating temperature of
the fuel cell, and a determine process of determining that the fuel
cell reaches the predetermined state which causes updating the
first impedance value, when the operating temperature of the fuel
cell is within a predetermined temperature range.
15. The control method according to claim 14, wherein the determine
process of determining that the fuel cell reaches the predetermined
state which causes updating the first impedance value, when the
operating temperature of the fuel cell is within the predetermined
temperature range during a predetermined time period.
16. The control method according to any one of claims 13, wherein
the update process is a process of updating the first impedance
value with reflecting a difference between the present value and
the original value in order to reduce a difference between the
present value and the updated first impedance value.
17. The control method according to claim 16, wherein the update
process is a process of updating the first impedance value by using
a correction strength that express a extent of reflection of the
difference between the present value and the original value.
18. The control method according to claim 17, further comprising:
an initialization history detection process of detecting a history
of initialization of the storage portion; and a correction strength
change process of changing the correction strength so that the
extent of reflection of the difference between the present value
and the original value becomes large when the history is detected
in the initialization history detection process.
19. The control method according to claim 16, wherein the storage
potion is a first storage portion, and the control method further
comprises an initialization history detection process of detecting
a history of initialization of the first storage portion; and a
setting value process of setting a secondary initial value, which
is larger than an initial value of the first impedance value that
is stored in a second storage portion in advance, as the original
value when a history of initialization of the first storage portion
is detected, wherein the update process is restarted and uses the
secondary initial as the initial value of the first impedance value
after the history of initialization of the first storage portion is
detected.
20. The control method according to claim 11, wherein the control
process includes a process of controlling a supply of a reaction
gas to the fuel cell on the basis of the first impedance value and
the second impedance value.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims the priority based on the
Japanese Patent Application No. (JP) 2014-230864 filed on Nov. 13,
2014, the disclosure of which is incorporated by reference herein
in its entirety.
BACKGROUND
[0002] 1. Field
[0003] The present invention relates to a fuel cell system and a
control method of a fuel cell system.
[0004] 2. Related Art
[0005] A polymer electrolyte fuel cell. (hereinafter, simply called
a "fuel cell") has a thin film of a solid polymer that shows
excellent proton conductivity in a wet state, and the moisture
status inside the fuel cell affects the power generation
efficiency. In a fuel cell system, in some cases, the impedance
that expresses the internal resistance of the fuel cell is measured
to detect the change in the moisture status inside the fuel cell
(for example, JP2013-110019A)
[0006] It is known that the internal resistance of a fuel cell also
changes due to aging degradation of the fuel cell. Therefore, when
a fuel cell undergoes aging degradation, the correlation between
the impedance of the fuel cell and the moisture status inside the
fuel cell changes, which may make it impossible to accurately
detect the moisture status of the fuel cell. From the past, in
order to apply to the operation control for the fuel cell, a
technology that may detect not only the moisture status inside the
fuel, but, also accurately detect the current status of the fuel
cell is desired.
SUMMARY
[0007] In order to solve at least part of the problem described
above, the present invention may be implemented in the aspects
described below.
[0008] (1) According to a first aspect of the present invention, a
fuel cell system is provided. The fuel cell system may include a
fuel cell, an impedance measurer, and a controller. The impedance
measurer may measure the impedance of the fuel cell. The controller
may perform an operation control of the fuel cell. The controller
may obtain a first impedance value that expresses the impedance of
the fuel cell in a predetermined state, and may acquire a second
impedance value that expresses the impedance of the fuel cell
measured by the impedance measurer during the operation control of
the fuel cell, and may perform the operation control of the fuel
cell using the first impedance value and the second impedance
value. According to the fuel cell system of this aspect, the state
of the fuel cell that includes, for example the wet state inside
the fuel cell may be detected accurately by using the first
impedance value and the second impedance value, and more
appropriate operation control in accordance with the state of the
fuel cell may be performed.
[0009] (2) In the fuel cell system of above aspect, the controller
may correct the second impedance value using the first impedance
value, and performs the operation control of the fuel cell on the
basis of the second impedance value after correction. According to
the fuel cell system of this aspect, since the second impedance
value is adjusted on the basis of the first impedance value, the
state of the fuel cell may be detected more accurately.
[0010] (3) The fuel cell system of the above aspect may further
include a storage portion for storing the first impedance value,
and the controller may execute an update process that updates the
first impedance value stored in the storage portion when the fuel
cell reaches the predetermined state during the operation control
of the fuel cell, in the update process, the controller may read
the first impedance value from the storage portion as an original
value, obtain the impedance of the fuel cell as a present value by
the impedance acquisition portion, calculate an updated first
impedance value by using the original value and the present value,
and store the updated first impedance value in the storage portion
as the first impedance value. According to the fuel cell system of
this aspect, since the first impedance value may be sequentially
updated, the value of the first impedance value is adjusted in a
better way, Therefore, the accuracy of detection of the state of
the fuel cell on the basis of impedance may be further
improved.
[0011] (4) In the fuel cell system of the above aspect may further
include a temperature detect portion that detects an operating
temperature of the fuel cell, and the controller may determine that
the fuel cell reaches the predetermined state when the operating
temperature of the fuel cell is within a predetermined temperature
range, and executes the update process. According to the fuel cell
system of this aspect, when the fuel cell is in a temperature state
that is suitable for measuring the impedance, the present value for
updating the first impedance value may be acquired, and thus, the
reliability of the value of the first impedance value may be
improved.
[0012] (5) In the fuel cell system of the above aspect, the
controller may determine that the fuel cell reaches the
predetermined state when the operating temperature of the fuel cell
is within the predetermined temperature range during a
predetermined time period, and executes the update process.
According to the fuel cell system of this aspect, the fuel cell may
acquire the present value when the temperature status suitable for
the measurement of the impedance is continued, and thus, the
acquisition of the present value immediately after the state in
which the fuel cell is in a remarkably high temperature may be
prevented, and a decline in the reliability of the value of the
first impedance value may also be prevented.
[0013] (6) In the fuel cell system of the above aspect, the
controller may update the first impedance value with reflecting a
difference between the present value and the original value so that
a difference between the present value and the updated first
impedance value is reduced. According to the fuel cell system of
this aspect, the value of the first impedance value is more
optimized.
[0014] (7) In the fuel cell system of the above aspect, the
controller may update the first impedance value by using a
correction strength that express a extent of reflection of the
difference between the present value and the original value in the
update process. According to the fuel cell system of this aspect,
the learning speed for adjustment of the first impedance value may
be controlled by changing the correction strength.
[0015] (8) The fuel cell system of the above aspect may further
include an initialization detector for detecting a history of
initialization of the storage portion, and the controller may
change the correction strength so that the extent of reflection of
the difference between the present value and the original value
becomes large when the history of initialization of the storage
portion is detected by the initialization detector. According to
the fuel cell system of this aspect, the learning speed of the
first impedance value after the initialization of the storage
contents of the storage portion may be improved, and the time
period until the recovery of the first impedance value to a value
close to the value before initialization of the storage portion is
reduced.
[0016] (9) In the fuel cell system of the above aspect, the storage
portion is a first storage portion, and the fuel cell system of the
above aspect may further comprise a second storage portion for
storing an initial value of the first impedance value; and an
initialization detector for detecting a history of initialization
of the first storage portion, and the controller may set a value
that is larger than the initial value of the first impedance value
stored in the second storage portion as the original value, and
restart the update of the first impedance value in the update
process, when a history of initialization of the first storage
portion is detected by the initialization detector. According to
the fuel cell system of this aspect, the time period until the
recovery of the first impedance value to a value close to the value
before initialization of the first storage portion is reduced.
[0017] (10) The fuel cell system of the above aspect may further
include a reaction gas supply portion for supplying reaction gas to
the fuel cell, and the controller may control the reaction gas
supply portion in the operation control of the fuel cell using the
first impedance value and the second impedance value. According to
the fuel cell system of this aspect, the supply of the reaction gas
to the fuel cell is performed more appropriately depending on the
current impedance of the fuel cell.
[0018] Not all of the plurality of components of each of the
above-described forms of the present invention are necessary, and
in order to resolve some or all of the above-described issues, or
to realize some or all of the above-described effects, some of the
plurality of components may be appropriately changed, deleted,
substituted with other new components, or some of the restricted
contents may be deleted. Moreover, in order to resolve some or all
of the above-described issues, or to realize some or all of the
above-described effects, some or all of the technical
characteristics described in one of the embodiments of the present
invention may be combined with some or all of the technical
characteristics included in the above-described other forms of the
present invention to result in an independent form of the present
invention.
[0019] The present invention may also be implemented through
various forms other than a fuel cell system. For example, the
present invention may be implemented through forms, such as an
apparatus for measurement of impedance of a fuel cell and a
measurement method; a correction method; a method of controlling a
fuel cell system; a computer program for implementing such methods;
or a non-transitory recording medium in which such a computer
program is recorded.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a schematic diagram showing a configuration of a
fuel cell system according to a first embodiment;
[0021] FIG. 2 is a schematic diagram showing an electrical
configuration of a fuel cell system according to the first
embodiment;
[0022] FIG. 3 is an explanatory diagram for explaining impedance of
a fuel cell;
[0023] FIG. 4 is an explanatory diagram showing a flow of an
operation control of a fuel cell performed by a controller;
[0024] FIG. 5 is an explanatory diagram showing a flow of an
impedance correction reference value update process;
[0025] FIG. 6 is an explanatory diagram showing a flow of an
impedance acquisition process;
[0026] FIG. 7 is a schematic diagram showing an electrical
configuration of a fuel cell system according to a second
embodiment;
[0027] FIG. 8 is an explanatory diagram showing a flow of an
impedance correction reference value update process according to
the second embodiment; and
[0028] FIG. 9 is an explanatory diagram showing an effect when a
correction reference value is set in an alternate initial value in
place of an initial value;
DESCRIPTION OF THE EMBODIMENTS
A. First Embodiment
A1. Configuration of a Fuel Cell System
[0029] FIG. 1 is a schematic diagram showing a configuration of a
fuel cell system 100 according to a first embodiment of the present
invention. The fuel cell system 100 is mounted on a fuel cell
vehicle, and outputs the power to be used as driving power in
accordance with a request from a driver that is a user. The fuel
cell system 10 includes a controller 10, a fuel cell 20, a cathode
gas supply portion 30, an anode gas supply portion 50, and a
cooling medium supply portion 70.
[0030] The controller 10 is configured by a micro-computer having a
central processing unit and a main storage unit, and the controller
10 exerts various functions by reading and executing programs on
the main storage unit. The controller 10 has a function of
executing operation control of the fuel cell 20 that generates
power according to a request output to the fuel cell 20 by
controlling each configuring portion of the fuel cell system 100.
The controller 10 further has a function of an impedance processing
portion 15 that acquires and corrects the impedance of the fuel
cell 20 used in operation control of the fuel cell 20. The
operation control of the fuel cell 20 by the controller 10 and the
functioning of the controller 10 as the impedance processing
portion 15 are described later.
[0031] The fuel cell 20 is a polymer electrolyte fuel cell that
generates power by receiving a supply of hydrogen (anode gas) and
air (cathode gas) as the reaction gas. The fuel cell 20 has a
stacked structure in which a plurality of unit cells 21 are
stacked. Each unit cell 21 is a power-generating element that may
generate power individually as well, and includes a membrane
electrode assembly that is a power generator in which electrodes
are arranged on both surfaces of an electrolyte film, and two
separators (not shown in the figure) that sandwich the membrane
electrode assembly. The electrolyte film is configured by a solid
polymer thin film showing excellent proton conductivity in the wet
state when moisture is contained inside the fuel cell. The
electrodes of the membrane electrode assembly include a catalyst
layer and a gas diffusion layer.
[0032] The cathode gas supply portion 30 has a function of
supplying cathode gas to the fuel cell 20, and a function of
discharging the discharge water that is discharged from the cathode
side of the fuel cell 20 and the cathode exhaust gas to outside the
fuel cell system 100. The cathode gas supply portion 30 includes a
cathode gas pipe 31, an air compressor 32, an air flowmeter 33, and
an on-off valve 34 at the upstream side of the fuel cell 20. The
cathode gas pipe 31 is a pipe that is connected to the inlet at the
cathode side of the fuel cell 20. The air compressor 32 is
connected to the fuel cell 20 via the cathode gas pipe 31, and
supplies the air that is compressed by incorporating the outside
air to the fuel cell 20 as the cathode gas.
[0033] The air flowmeter 33 measures the amount of outside air
incorporated by the air compressor 32 at the upstream side of the
air compressor 32, and sends the measured value to the controller
10. By driving the air compressor 32 on the basis of the measured
value, the controller 10 controls the amount of supply of air to
the fuel cell 20. The on-off valve 34 is provided between the air
compressor 32 and the fuel cell 20. The on-off valve 34 is normally
in a closed state, and opens when air having a predetermined
pressure is supplied to the cathode gas pipe 31 from the air
compressor 32.
[0034] The cathode gas supply portion 30 includes a cathode exhaust
gas pipe 41, a pressure-regulating valve 43, and a pressure
measurement portion 44 at the downstream side of the fuel cell 20.
The cathode exhaust gas pipe 41 is a pipe that is connected to the
outlet at the cathode side of the fuel cell 20, and discharges the
discharge water and cathode exhaust gas to the outside of the fuel
cell system 100. The pressure-regulating valve 43 adjusts the
pressure of the cathode exhaust gas (back pressure at the
cathode-side of the fuel cell 20) in the cathode exhaust gas pipe
41. The pressure measurement portion 44 is provided at the
upstream-side of the pressure-regulating valve, measures the
pressure of the cathode exhaust gas, and sends the measured value
to the controller 10. The controller 10 adjusts the opening of the
pressure-regulating valve 43 on the basis of the measured value of
the pressure measurement portion 44.
[0035] The anode gas supply portion 50 has a function of supplying
anode gas to the fuel cell 20, a function of discharging the anode
exhaust gas that is discharged from the fuel cell 20 to the outside
of the fuel cell system 100, and a function of circulating the
anode gas within the fuel cell system 100. The anode gas supply
portion 50 includes an anode gas pipe 51, a hydrogen tank 52, an
on-off valve 53, a regulator 54, a hydrogen supply apparatus 55,
and a pressure measurement portion 56 at the upstream side of the
fuel cell 20. High-pressure hydrogen is filled in the hydrogen tank
52 for supply to the fuel cell 20. The hydrogen tank 52 is
connected to the inlet at the anode side of the fuel cell 20 via
the anode gas pipe 51.
[0036] The on-off valve 53, the regulator 54, the hydrogen supply
apparatus 55, and the pressure measurement portion 56 are provided,
in this order, to the anode gas pipe 51 from the upstream side (the
hydrogen tank 52-side), By controlling the opening and closing of
the on-off valve 53, the controller controls the inflow of hydrogen
from the hydrogen tank 52 to the upstream side of the hydrogen
supply apparatus 55. The regulator 54 is a pressure-reducing valve
for adjusting the pressure of hydrogen at the upstream side of the
hydrogen supply apparatus 55, and the opening thereof is controlled
by the controller 10. The hydrogen supply apparatus 55, for
example, is configured by an injector, which is a solenoid operated
on-off valve. The pressure measurement portion 56 measures the
pressure of hydrogen at the downstream side of the hydrogen supply
apparatus 55, and sends the measured value to the controller 10. By
controlling the drive cycle (opening/closing cycle) of the hydrogen
supply apparatus 55 on the basis of the measured value of the
pressure measurement portion 56, the amount of hydrogen supplied to
the fuel cell 20 is controlled.
[0037] The anode gas supply portion 50 includes an anode discharge
pipe 61, a gas-liquid separator 62, an anode gas circulation pipe
63, a hydrogen circulation pump 64, an anode discharge water pipe
65, a drain valve 66, and a pressure measurement portion 67 at the
downstream side of the fuel cell 20. The anode exhaust gas pipe 61
connects the anode-side outlet of the fuel cell 20 and the
gas-liquid separator 62. The anode exhaust gas pipe 61 is provided
with a pressure measurement portion 67. The pressure measurement
portion 67 measures the pressure of the anode exhaust gas in the
vicinity of fuel cell 20 hydrogen manifold outlet (anode-side back
pressure of fuel cell 20), and sends the measurement to the
controller 10.
[0038] The gas-liquid separator 62 is connected to the anode gas
circulation pipe 63 and the anode discharge water pipe 65. The
anode exhaust gas that flows into the gas-liquid separator 62
through the anode exhaust gas pipe 61 is separated into the gas
component and the water component by the gas-liquid separator 62.
In the gas-liquid separator 62, the gas component of the anode
exhaust gas is channeled into the anode gas circulation pipe 63,
and the water component is channeled into the anode discharge water
pipe 65.
[0039] The anode gas circulation pipe 63 is connected downstream
from the hydrogen supply apparatus 55 of the anode gas pipe 51. The
hydrogen circulation pump 64 is provided in the anode gas
circulation pipe 63, and the hydrogen included in the gas component
separated in the gas-liquid separator 62 is fed to the anode gas
pipe 51 by the hydrogen circulation pump 64.
[0040] The drain valve 66 is provided in the anode discharge water
pipe 65. The drain valve 66 opens and closes according to an
instruction from the controller 10. The controller 10 normally
keeps the drain valve 66 in the closed position, and opens the
drain 66 at a predetermined discharge water timing that has already
been set, or at the discharge timing of the inert gas present in
the anode exhaust gas. The downstream end of the anode drain pipe
65 mixes the anode-side waste water and the anode exhaust gas with
the cathode-side waste water and the cathode exhaust gas and merges
them into the cathode exhaust gas pipe 41 so that they may be
discharged (not shown in the drawing).
[0041] The cooling medium supply portion 70 includes a cooling
medium pipe 71, a radiator 72 a circulation pump 75, and two
temperature measurement portions 76a and 76b. The cooling medium
pipe 71 is a pipe for circulating the cooling medium for cooling
the fuel cell 20, and is configured by an upstream-side pipe 71a
and a downstream-side pipe 71b. The upstream-side pipe 71a connects
the outlet of the cooling medium flow path inside the fuel cell 20
and the inlet of the radiator 72. The downstream-side pipe 71b
connects the inlet of the cooling medium flow path inside the fuel
cell 20 and the outlet of the radiator 72.
[0042] The radiator 72 has a fan for pulling in outside air, which
cools the cooling medium through heat exchange between the cooling
medium pipe 71 and the outside air. The circulation pump 75 is
provided in the downstream-side pipe 71b, and is driven on the
basis of an instruction from the controller 10. The cooling medium
flows inside the cooling medium pipe 71 because of the driving
power of the circulation pump 75.
[0043] The first temperature measurement portion 76a is provided in
the upstream-side pipe 71a, and the second temperature measurement
portion 76b is provided in the downstream-side pipe 71b. The
controller 10 detects the cooling medium temperature in each pipe
71a and 71b by the two temperature measurement portions 76a and
76b, and detects the temperature of the fuel cell 20 from the
difference in the cooling medium temperature of each pipe 71a and
71b. The controller 10 controls the operating temperature of the
fuel cell 20 by changing the rotation speed of the circulation pump
75 based on the operating temperature of the fuel cell 20.
[0044] FIG. 2 is a schematic diagram showing the electrical
configuration of fuel cell system 100. The fuel cell system 100
includes a secondary cell 82, a DC/DC converter 84, a DC/AC
inverter 86, an impedance measurement portion 90, a first storage
portion 91, and a second storage portion 92. In the fuel cell
system 100, the fuel cell 20 is connected to the DC/AC inverter 86
via a DC line 81. The DC/AC inverter 86 is connected to a
three-phase AC motor 200 (hereinafter, simply called "motor 200"),
which is a source of drive power of the fuel cell vehicle. The
secondary cell 82 is connected to the DC line 81 via the DC/DC
converter 84.
[0045] The secondary cell 82 is composed of a lithium ion battery,
for example. The secondary cell 82 is charged by the output power
from the fuel cell 20 and the regenerative electric power from the
motor 200, allowing it to serve as a power source along with the
fuel cell 20. The DC/DC converter 84 variably adjusts the voltage
level of the DC line 81 based on an instruction from the controller
10, and thereby controls the current and voltage of the fuel cell
20, as well as the charging/discharging of the secondary cell 82.
The DC/AC inverter 86 converts the DC power from the fuel cell 20
and the secondary cell 82 into AC power to supply to the motor 200.
Also, when the motor 200 produces regenerative electric power, it
converts the regenerative power into DC power.
[0046] The impedance measurement portion 90 corresponds to a
subordinate concept of the impedance measurer of the present
invention. The impedance measurement portion 90 applies the AC
impedance method to obtain the impedance from each unit cell 21 and
the fuel cell 20. It then outputs this impedance to controller 10.
Impedance measurement portion 90 is equipped with an AC power
supply, and applies high frequency AC to each unit cell 21 and the
fuel cell 20 (for example, the number of kHz-MHz) to measure the DC
resistance (described later) within each unit cell 21 impedance
according to a command from controller 10. Hereinafter, this is
referred to as simply "impedance of the fuel cell 20" without
differentiating between the impedances obtained from each unit cell
21. The controller 10 uses the impedance of the fuel cell 20 as
provided by the impedance measurement portion 90 to control the
operation of fuel cell 20.
[0047] The first storage portion 91 is composed, for example, of a
volatile memory such as SRAM. The first storage portion 91 stores
information in a rewritable form, and allows it to be updated. The
information stored in the first storage portion 91 is retained even
after the fuel cell system 100 ceases operation, by receiving power
from secondary cell 82. The first storage portion 91 stores the
reference correction value Z.sub.s which is used to correct the
impedance in the impedance acquisition process as explained later.
The correction reference value Z.sub.s is then updated during the
impedance correction reference value updating process as described
later. The second storage portion 92 is composed, for example, of a
nonvolatile memory such as ROM to store the information that does
not require updating. The first storage portion 91 stores the
initial value Z.sub.0 for the correction reference value Z.sub.s
which is used to correct impedance in the impedance acquisition
process executed to control the operation of the fuel cell 20. The
reference correction value Z.sub.s and initial value Z.sub.0 are
described along with an explanation of the impedance correction
process and impedance correction reference value update
process.
A2. Impedance of the Fuel Cell
[0048] FIG. 3 explains the impedance of the fuel cell. In the
section (a) of FIG. 3, an example of a Nyquist plot (Cole-Cole
plot) obtained from a general polymer electrolyte fuel cell based
on the AC impedance method is shown. In the section (b) of FIG. 3,
a graph of the aging of the DC component in the fuel cell impedance
is illustrated. The impedance of the fuel cell includes the AC
resistance component, represented by the semi-circular portion of
the Nyquist plots, and the DC resistance component, represented by
the straight-line portion in the section (a) of FIG. 3. As
described above, the impedance measurement portion 90 in this
design uses a high-frequency alternating current to measure the DC
resistance of the impedance.
[0049] The DC resistance component of the impedance includes
components such as electrolyte membrane resistance and proton
transfer resistance that may vary according to the fuel cell
moisture content in the fuel cell in the section (b) of FIG. 3.
Therefore, by obtaining the correlation between the fuel cell
moisture content and DC resistance beforehand, it is possible to
determine the moisture content and moisture status of the fuel cell
based on the DC resistance component of impedance.
[0050] The DC resistance component of impedance includes components
such as the resistance of conductive members such as the gas
diffusion layer and the separator, and the contact resistance
between these conductive members, values which are hardly affected
by the fuel cell moisture content. These components tend to
increase over time since they are affected by factors such as
oxidation of the conductive members or aging of the fuel cell stack
fastenings. In the fuel cell system 100 in this first embodiment,
the value of fuel cell 20 impedance, which is used in the operation
control of fuel cell 20, is corrected to reduce the influence of
aging so that the value of fuel cell 20 impedance more accurately
represents moisture content which is amount of moisture included in
the fuel cell 20.
A3. Fuel Cell System Operation Control
[0051] FIG. 4 shows the sequence of operation control for fuel cell
20 as executed by controller 10. In step S10, the impedance
processing portion 15 in the controller 10 executes the impedance
correction reference value updating process to update the
correction reference value Z.sub.s which is used to correct
impedance in the impedance acquisition process in step S40. The
correction reference value and the correction reference value
update process will be described later.
[0052] In step S20, the controller 10 detects the user's output
request. In step S30, the controller 10 determines the target power
to output to the fuel cell 20 based on the user's output request.
In step S40, the impedance processing portion 15 executes impedance
acquisition processing to obtain the impedance of the fuel cell 20
by the impedance measurement portion 90. The impedance acquisition
processing uses the correction reference value Z.sub.s to correct
the raw measured value for impedance. The impedance acquisition
processing will be described later.
[0053] In step S45, the controller 10 executes the impedance
determination process and switches the reactant gas supply control
for the fuel cell 20 to either normal operation or increasing
moisture operation based on the corrected impedance value. When the
corrected impedance is less than or equal to a predetermined value,
the controller 10 executes the normal operation in step S50 for the
fuel cell 20 in wet state, meaning there is sufficient moisture
content. On the other hand, when the corrected impedance is greater
than or equal to the predetermined value, controller 10 executes
the increasing moisture operation in step S55 for the fuel cell 20
in dry state, meaning there is insufficient moisture content.
[0054] In the step S50 normal operation, the controller 10 uses a
predetermined control map that is prepared in accordance with the
target output determined in step S20, to set a target pressure and
a target flow rate to supply reactant gas to fuel cell 20.
Hereafter, the target pressure of the reactant gas under normal
operations is referred to as the "first target pressure". The
controller 10 start the supplying the reactant gas to cathode gas
supply portion 30 and anode gas supply portion 50 at the target
flow rate and first target pressure.
[0055] In the increasing moisture operation in step S55, the
controller 10 determines the target flow rate for the reactant
gases just as with normal operations, and sets the target pressure
higher than that of the first target pressure for normal
operations, hereinafter referred to as the "second target
pressure". The controller 10 make the cathode gas supply portion 30
and the anode gas supply portion 50 start the reactant gas supply
operation according to the target flow rate and second target
pressure. In the increasing moisture operation, the reactant gas is
supplied to fuel cell 20 at a pressure higher than that of normal
operations. This allows the partial pressure of water vapor in the
exhaust gas to decrease, which makes it possible to reduce the
amount of moisture carried away from fuel cell 20 by the reactant
gas. This means that the moisture content in fuel cell 20 may be
increased higher than that of normal operations.
[0056] The controller 10 repeats the processes of steps S10-S55
until the operation of the fuel cell system 100 is terminated in
step S60. Thus, in the fuel cell system 100 in this first
embodiment, the moisture content of fuel cell 20 is determined
based on the impedance of fuel cell 20. In the case that the fuel
cell 20 is determined to be in a dry state, the increasing moisture
operation is executed to increases the moisture content of fuel
cell 20 in the reactant as supply operation. Accordingly, decrease
in power generation efficiency due to moisture shortage in the fuel
cell 20 is suppressed.
[0057] FIG. 5 shows the sequence of the impedance correction
reference value updating process executed by the impedance
processing portion 15 in step S10 in FIG. 4. The correction
reference value Z.sub.s corresponds to a subordinate concept of
first impedance value in the present invention. When the impedance
of fuel cell 20 is corrected, the correction reference value
Z.sub.s is used as the reference value. The correction reference
value Z.sub.s represents the impedance of fuel cell 20 in a
predetermined reference condition where the electrolyte membrane is
confirmed to he in wet state.
[0058] The correction reference value Z.sub.s is sequentially
updated based on the impedance obtained by impedance measurement
portion 90 when the fuel cell 20 is in the reference condition.
[0059] In step S210 impedance processing portion 15 determines
whether or not fuel cell 20 is in the predetermined reference
condition based on its operating temperature. The impedance
processing portion 15 determines that fuel cell 20 is in the
reference state when both of the following conditions are
satisfied: (a), (b).
[0060] (a) the operating temperature of fuel cell 20 is equal or
greater than T.sub.1 and less than T.sub.2.
[0061] (b) the operating temperature of fuel cell 20 is equal or
less than T .sub.3 for a predetermined period p.
[0062] In the condition (a), the intention of the condition that
the operating temperature of fuel cell 20 is greater than T.sub.1
is to suppress to add the noise, such as the diffusion resistance
of the reactant gas to the impedance measurement of the fuel cell
20. The temperature assigned as T.sub.1 may be determined
experimentally in advance based on the frequency of the alternating
current used to measure impedance. In this first embodiment,
T.sub.1 is 55.degree. C.
[0063] In the condition (a), the intention of the condition that
the operating temperature of fuel cell 20 is less than T.sub.2 is
to ensure that the current operating temperature of fuel cell 20 is
not causing the electrolyte membrane to dry out. The temperature
assigned as T.sub.2 may be determined experimentally in advance, as
a temperature unlikely to cause the electrolyte membrane to dry
out. In this first embodiment, T.sub.2 is 60.degree. C.
[0064] The condition (b) intends to ensure that the operating
temperature of fuel cell 20 is not the significantly high
temperature, for example about 90.degree. C., just before. This is
because immediately after the operating temperature of the fuel
cell 20 is the significantly high temperature, the electrolyte
membrane may still be in a dry state. The temperature assigned as
T.sub.3 in the condition (b) may be determined based on the average
operating temperature of fuel cell 20, and like T.sub.2 in the
condition (a), it may be determined experimentally in advance, as a
temperature unlikely to cause the electrolyte membrane to dry out.
In this first embodiment, T.sub.3 is 60.degree. C., which is same
as temperature T.sub.2 in the condition (a).
[0065] The predetermined period p in the condition (b) shall be
preferably approximately the period when the dry state of the
electrolyte membrane is canceled when the operating temperature of
the fuel cell 20 returns from significantly higher temperature, for
example about 90.degree. C., to normal temperature, for example
about 60.degree. C. In this first embodiment, the predetermined
period p is 60 seconds.
[0066] If at least one of the conditions (a) or (b) is not
satisfied, as the case that the fuel cell 20 is not under
prescribed standard condition, the impedance processing portion 15
terminates the impedance correction reference value update process
as shown NO of step S210. In this case, the correction reference
value Z.sub.s does not get updated, and the operation control of
the fuel cell 20 continues beyond the step S20 of FIG. 3.
[0067] If at least one of the conditions (a) or (b) is satisfied,
the impedance processing portion 15 determines that the fuel cell
20 is under prescribed standard condition as shown by YES of step
S210. In this case, the impedance of the fuel cell 20 used for
updating the correction reference value Z.sub.s is obtained from
the impedance measurement portion 90 in step S220. Hereafter, the
impedance of the fuel cell 20 obtained in step S220 is called as
the "the present value Z.sub.c".
[0068] In step S230, the correction reference value Z.sub.s saved
in the first storage portion 91 in FIG. 2 is read out as the
previous value Z.sub.p (Z.sub.p=Z.sub.s) by the impedance
processing portion 15. If the impedance correction reference value
update process is for the first time, the initial value Z.sub.o of
the correction reference value Z.sub.s saved in the second storage
portion 92 is set as the previous value Z.sub.p. The initial value
Z.sub.o is a value determined experimentally beforehand and
represents the impedance of the fuel cell 20 when it is under
prescribed condition at the time of shipping from the factory. The
previous value Z.sub.p corresponds to the subordinate concept of
the original value in the present invention.
[0069] In step S240, the impedance processing portion 15 updates
the correction reference value Z.sub.s in order to mitigate the
difference between the previous value Z.sub.p and the present value
Z.sub.c in the updated correction reference value Z.sub.s by
performing a correction which reflects this difference to the
previous value Z.sub.p that is the present correction reference
value Z.sub.s. Specifically, in order to obtain the new correction
reference value Z.sub.s, the difference obtained by subtracting the
previous value Z.sub.p from the present value Z.sub.c is multiplied
with a coefficient .alpha., and adds to the previous value Z.sub.p
as shown in the following formula (A). The coefficient .alpha. is
less than 1.
Z.sub.s=Z.sub.p+.alpha.(Z.sub.c-Z.sub.p) (A)
[0070] The coefficient .alpha. is a so-called the smoothing factor,
and it corresponds to a subordinate concept of the correction
strength which expresses an extent that the difference between the
present value Z.sub.c and the previous value Z.sub.p is reflected
to the correction reference value Z.sub.s. By multiplying the
coefficient .alpha. with the difference between the present value
Z.sub.c and the previous value Z.sub.p, even if the present value
Z.sub.c accidentally is obtained as an extremely large value due to
factors such as measurement error etc., it becomes possible to
prevent the correction reference value Z.sub.s being immediately
affected by such effect. Moreover, the above formula (A) may be
expanded as the following formula (A'). As shown in the formula
(A') below, the above correction due to the coefficient .alpha.,
may be interpreted as applying the weightage of the present value
Z.sub.c and the previous value Z.sub.p.
Z.sub.s=.alpha.Z.sub.c+(1-.alpha.)Z.sub.p (A')
[0071] The impedance processing portion 15 updates by rewriting the
correction reference value Z.sub.s as the corrected correction
reference value Z.sub.s of the first storage portion 91 shown in
FIG. 2, and ends the impedance correction reference value updating
process. Subsequently, the operation control of the fuel cell 20 by
the controller 10 is continued beyond step S20 in FIG. 3.
[0072] Thus, in this first embodiment, in the reference state in
which it is guaranteed that the wet state of the electrolyte
membrane of the fuel cell 20 is excellent, the present value
z.sub.p is acquired in order to update the correction reference
value Z.sub.s. Therefore, the reliability of the correction
reference value Z.sub.s is enhanced as a reference value for
correcting the impedance. Also, the correction reference value
Z.sub.s is sequentially updated, and the status change of the fuel
cell 20 is reflected properly in real time in the correction
reference value Z.sub.s. Therefore, the reliability of the
impedance of the correction of the impedance in the impedance
acquisition process described below is ensured.
[0073] FIG. 6 is an explanatory diagram depicting the flow of the
impedance acquisition process in step S40 in FIG. 4 executed by the
impedance processing portion 15. In step S310, the impedance
processing portion 15 acquires the measured value Z.sub.m of the
present impedance in the fuel cell 20 by the impedance measuring
portion 90. The measured value Z.sub.m corresponds to the
subordinate concept of the second impedance value in the present
invention. In step S320, the impedance processing portion 15 reads
the initial value Z.sub.0 of the correction reference value Z.sub.s
from the second storage portion 92 in FIG. 2.
[0074] In step S330, the impedance processing portion 15 corrects
the measured value Z.sub.m by using the correction reference value
Z.sub.s and the initial value Z.sub.0. More specifically, the
impedance processing portion 15 performs the correction by
subtracting the difference between the correction reference value
Z.sub.S and the initial value Z.sub.0 from the measured value
Z.sub.m. With this correction, the impedance processing portion 15
acquires the determination impedance Z.sub.j, which is the
corrected impedance used in the determination processing in step
S45 as shown in formula (B) below.
Z.sub.j=Z.sub.m(Z.sub.s-Z.sub.0) (B)
[0075] The difference (Z.sub.s-Z.sub.0) between the correction
reference value Z.sub.s and the initial value Z.sub.0 in the above
formula (B) corresponds to the increased amount .DELTA.D of the
impedance due to aged deterioration shown in the graph in the
section (B) of FIG. 3. In other words, the determination impedance
Z.sub.j obtained from the above correction corresponds to a value
from which the increased component of the impedance due to aging
has been removed, and has been optimized so as to appropriately
indicate the moisture content in the present fuel cell 20.
[0076] As described above, in the fuel cell system 100 of the this
first embodiment, the moisture condition inside the fuel cell 20 is
determined based on the determination impedance Z.sub.j obtained by
correcting the measured value Z.sub.m corresponding to the
subordinate concept of the second impedance value by using the
correction reference value Z.sub.s corresponding to the subordinate
concept of the first impedance value. Therefore, operation control
of the fuel cell 20 according to the moisture condition in the fuel
cell 20 is more appropriately performed.
B. Second Embodiment
[0077] FIG. 7 is a schematic view showing the electrical
configuration of a fuel cell system 100A as the second embodiment
of the present invention. Except for providing a point provided
with an energization state monitoring portion 93, and storing the
alternative initial value Z.sub.1, in addition to the initial value
Z.sub.0, in the second storage portion 92, the configuration of the
fuel cell system 100A in the second embodiment is substantially the
same as the configuration of the fuel cell system 100 in the first
embodiment. The operation control of the fuel cell 20 in the fuel
cell system 100A in the second embodiment, except for the fact that
the flow of the impedance correction reference value updating
processing is different, is substantially the same as the operation
control of the first embodiment.
[0078] As described in the first embodiment, the first storage
portion 91 holds the stored information by the electric power of a
secondary cell 82 during the operation stop of the fuel cell system
100A. The energization state monitoring portion 93 monitors the
status of energization from the secondary cell 82 to the first
storage portion 91.
[0079] There is a possibility that the energization of the first
storage unit 91 from the secondary cell 82 gets interrupted because
of unforeseen circumstances such as, for example, when the
secondary cell 82 is removed from the fuel cell vehicle for the
maintenance of the fuel cell vehicle, or if the amount of charge of
the secondary cell 82 is insufficient. The energization state
monitoring portion 93, during the operation stoppage of the fuel
cell system 100A, if the disruption of the power supply to such
first storage section 91 is detected, measures the duration of such
disruption. The energization state monitoring portion 93, after
starting of the fuel cell system 100A, transmits the detection
result to the controller 10.
[0080] FIG. 8 is an explanatory diagram showing the flow of the
impedance correction reference value updating process of the second
embodiment that is executed by the impedance processing portion 15.
The impedance correction reference value updating process in the
second embodiment, except for executing the processes in steps S201
and S202 before the step S210, is substantially same as in the
first embodiment. In FIG. 8, for convenience, the illustration of
the processing after the step S210 has been omitted.
[0081] In step S201, the impedance processing portion 15 checks for
the existence of the history whether the stored information in the
first storage section 91 was reset, in other words initialized, on
the basis of the detection result from the energization state
monitoring portion 93. In the case that the impedance processing
portion 15, with the help of the energization state monitoring
portion 93, detects the disruption of the power supply to the first
storage portion 91 during the stoppage of the fuel cell system 100,
and the duration of the interruption is longer than a predetermined
time, the impedance processing portion 15 determines that the
information stored in the first storage portion 91 has been reset.
In this case, the impedance processing portion 15 executes the
process of step S202 as shown YES of step S201.
[0082] In case that the energization state monitoring portion 93
does not detect a disruption in power supply from the secondary
cell 82 to the first storage portion 91 that is longer than the
predetermined period, the impedance processing portion 15
determines that the information stored in the first storage portion
91 has been preserved. In this case, the impedance processing
portion 15 starts the processing after step S210 in FIG. 4
described in the first embodiment.
[0083] In step S202, the impedance processing portion 15 executes
the process for changing the process to expedite the recovery of
the correction reference value Z.sub.s that was reset. The
impedance processing portion 15 increases the value of the
coefficient .alpha., which is the correction strength contained in
the formula (A) described above, more than in the process of
previous time. For example, if the coefficient .alpha., is 0.5, it
is increased to 0.8. With this, during the updating of the
correction reference value Z.sub.s in step S240 in FIG. 5, the
degree of the difference between the present value Z.sub.c and
previous value Z.sub.p getting reflected is increase, the number of
updates before the correction reference value Z.sub.S reaches a
value before the reset becomes less, and the learning period of
correction reference value Z.sub.s is shortened.
[0084] Further, the impedance processing portion 15 also sets the
correction reference value Z.sub.s to alternate initial value
Z.sub.1 instead of to the initial value Z.sub.0. The alternate
initial value Z.sub.1 is an average value between the initial value
Z.sub.0 with the fuel cell 20 at the time of factory shipping as
the reference, and the post-durability test reference impedance
Z.sub.2 that represents an impedance when the fuel cell 20 is in a
specific reference state after durability test assuming a use of
long period, for example about few tens of years. Alternate initial
value Z.sub.1 is determined by the following formula (C).
Z.sub.1=(Z.sub.0+Z.sub.2)/2 (C)
[0085] FIG. 9 is an explanatory diagram showing the effect when the
correction reference value Z.sub.s is set to the alternate initial
value Z.sub.1 instead of the initial value Z.sub.0. FIG. 9
exemplifies a graph in which the vertical axis shows the correction
reference value Z.sub.s, and the horizontal axis shows the updated
count of the correction reference value Z.sub.s. The value LV of
the vertical axis in the graph of FIG. 9 indicates a value wherein
the correction reference value Z.sub.s before the erasure
immediately before the stored information in the first storage
portion 91 is reset, that is, a value where the correction
reference value Z.sub.s shall be restored.
[0086] In case the first correction reference value Z.sub.s after
resetting the of the first storage portion 91 is set to initial
value Z.sub.0, as shown in dot line graph Ga, the correction
reference value Z.sub.s increases each time the updating process of
step S240 is repeated, and continues to approach the value LV
before the reset of the first storage portion 91. In case the first
correction reference value Z.sub.s is set to the post-durability
test reference impedance Z.sub.2, as shown in dashed-line graph Gb,
the correction reference value Z.sub.s decreases with each
repetition of the update process of step S240, and continues to
approach the value LV before the reset of the first storage portion
91.
[0087] If the first correction reference value Z.sub.s is set to
alternate initial value Z.sub.1, the correction reference value
Z.sub.s from the beginning becomes a value nearer to the value LV
which is the value before reset. Therefore, it is possible to reach
the value LV before reset in less number of updates compared to the
case of setting to the above initial value Z.sub.0 or
post-durability test reference impedance Z.sub.2 as shown by the
solid line graph Gc. Further, it is not necessary for alternative
initial value Z.sub.1 to be the average value between the initial
value Z.sub.0 and post-durability test reference impedance Z.sub.2,
and as shown in the following inequality equation (D), it may be a
value that is greater than the initial value Z.sub.0, and smaller
than the post-durability test reference impedance Z.sub.2.
Z.sub.0<Z.sub.1<Z.sub.2 (D)
[0088] As described above, if it is a fuel cell system 100A in the
second embodiment, even if the reference correction value Z.sub.s
of the first storage portion 91 is lost, the period till its
recovery is shortened. In addition, if it is a fuel cell system
100A in the second embodiment, it is possible to achieve the same
effect as that described in the first embodiment.
C. Modifications
C1. Modification 1:
[0089] In each of the above embodiments, the controller 10 performs
the operation control of the fuel cell 20 by using the impedance
Z.sub.j for determining the corrected value of the measured value
Z.sub.m of the impedance corresponding to the subordinate concept
of the second impedance value by using the reference correction
value Z.sub.s corresponding to the subordinate concept of the first
impedance value. Alternatively, the controller 10 need not perform
the correction process to correct the measured value Z.sub.m by
using the reference correction value Z.sub.m. The controller 10 may
perform the operation control of the fuel cell 20 by using the
reference correction value Z.sub.s and the measured value Z.sub.m.
For example, controller 10, by changing the threshold value of the
determination process in step S10 as per the reference correction
value Z.sub.s, may also execute the determination process of step
S10 by using the measured value Z.sub.m as the impedance for
determination.
C2 Modification 2:
[0090] In each of the above embodiments, as an operation control of
the fuel cell 20, and depending on the impedance of the fuel cell
20, the controller 10 performs the supply control of the reactant
gas to the fuel cell 20 by switching between normal operation and
increasing moisture operation. In contrast to this, the controller
10, as an operation control of the fuel cell 20, may also perform
other operation controls. For example, the controller 10 may also
perform reactant gas supply control that varies the supply flow
rate or supply pressure of the reactant gas as per the impedance of
the fuel cell 20. Alternatively, the controller 10, depending on
the impedance of the fuel cell 20, may also execute operation
control for determining the execution timing for the scavenging
process for scavenging the interior of the fuel cell 20. The
controller 10 may perform the operation control for controlling the
operating temperature of the fuel cell 20 by changing the
circulation flow rate of the coolant as per the impedance of the
fuel cell 20.
C3. Modification 3:
[0091] In each of the above-described embodiments, the controller
10 executes operation control of the fuel cell 20 by using the
impedance of the fuel cell 20 as the value that expresses the wet
state inside the fuel cell 20. In contrast, the controller 10 may
execute operation control of the fuel cell 20 by using the
impedance of the fuel cell 20 as the value that expresses any other
state of the fuel cell 20. For example, the controller 10 may use
the impedance of the fuel cell 20 as a value that expresses the
movement resistance of protons in the fuel cell 20, and execute
operation control in which the desired output of the fuel cell 20
is changed according to the impedance of the fuel cell 20.
C4. Modification 4:
[0092] In each of the above-described embodiments, the impedance
processing portion 15 uses the present value Z.sub.c with respect
to the correction reference value Z.sub.s, and performs a
correction process of reflecting the difference between the present
value Z.sub.c and the previous value Z.sub.p so as to reduce the
difference between the present value Z.sub.c and the previous value
Z.sub.p. In contrast, the impedance processing portion 15 may
perform any other correction by using the present value Z.sub.c
with respect to the correction reference value Z.sub.s. The
impedance processing portion 15 may also perform a correction
process of substituting the correction reference value Z.sub.s in
the present value Z.sub.c each time the present value Z.sub.c
acquired. If there is a difference between the present value
Z.sub.c and the previous value Z.sub.p, the impedance processing
portion 15 may perform correction to increase or reduce the
correction reference value Z.sub.s only by as much as the
predetermined correction amount. The impedance processing portion
15 may also perform an arithmetic processing of acquiring the
correction reference value Z.sub.s by subtracting the difference
between the present value Z.sub.c and the previous value Z.sub.p
from the present value Z.sub.c, without multiplying with the
coefficient .alpha..
C5. Modification 5:
[0093] In each of the above-described embodiments, the impedance
processing portion 15 performs the judgment of whether or not the
fuel cell 20 is in the predetermined reference state on the basis
of the operating temperature of the fuel cell 20. In contrast, the
impedance processing portion 15 may perform the judgment of whether
or not the fuel cell 20 is in the predetermined reference state on
the basis of a parameter other than the operating temperature of
the fuel cell 20. For example, when the fuel cell 20 continues with
the generation of power within a predetermined range of the present
value for a predetermined time period, the impedance processing
portion 15 may determine that the fuel cell 20 is in a
predetermined reference state.
C6. Modification 6:
[0094] In the fuel cell system 100A according to the
above-described second embodiment, the process of increasing the
coefficient .alpha. and the process of setting the correction
reference value Z.sub.s in the alternate initial value Z.sub.1 are
executed when the information stored in the first storage portion
91 is reset. In contrast, only one of the process of increasing the
coefficient .alpha. and the process of setting the correction
reference value Z.sub.s in the alternate initial value Z.sub.1 may
be executed when the information stored in the first storage
portion 91 is reset.
C7. Modification 7:
[0095] In the fuel cell system 100A according to above-described
second embodiment, the impedance processing portion 15 performs the
process of increasing the coefficient .alpha. when the information
stored in the first storage portion 91 is reset. In contrast, the
impedance processing portion 15 may perform the process of changing
the coefficient .alpha. in various conditions rather than only when
the information stored in the first storage portion 91 is reset.
For example, the impedance processing portion 15 may change the
coefficient .alpha. when an instruction for changing the learning
speed of the correction reference value Z.sub.s is received from
the user, and the impedance processing portion complies with the
instruction.
C8. Modification 8:
[0096] In each of the above embodiments, rather than
differentiating the impedance of each unit cell 21 acquired by the
impedance measurement portion 90, it is explained as the impedance
of the fuel cell 20. In the fuel cell systems 100 and 100A
according to each of the above-described embodiments, the operation
control of the fuel cell 20 may be executed on the basis of the
impedance of each unit cell 21. For example, when it is detected
that the impedance of some of the unit cells 21 is higher than that
of the other unit cells 21, an operation control to temporarily
increase the output current of the fuel cell 20, or an operation
control to temporarily increase the flow of the reaction gas may be
executed.
C9. Modification 9:
[0097] The fuel cell systems 100 and 100A according to each of the
above-described embodiments are mounted on a fuel cell vehicle. In
contrast, the fuel cell systems 100 and 100A may not necessarily be
mounted on a fuel cell vehicle, for example, the fuel cell systems
may be installed in a building or facility.
C10. Modification 10:
[0098] In the fuel cell systems 100 and 100A according to each of
the above-described embodiments, a polymer electrolyte fuel cell is
used as the fuel cell 20. In contrast, the fuel cell 20 may not be
a polymer electrolyte fuel cell, but may be a fuel cell of various
other types.
[0099] The present invention is not restricted to the
above-described embodiments, examples, and modifications, and may
be implemented in various configurations as long as the jist of the
invention is not lost. For example, the technical characteristics
described in the embodiments, examples, and modifications
corresponding to the technical characteristics in each form
described in the SUMMARY OF INVENTION column may be appropriately
substituted or combined together in order to resolve some or all of
the above-described issues, or to realize some or all of the
above-described effects. Moreover, if the technical characteristics
are not described as compulsory in the SPECIFICATIONs, they may be
deleted appropriately. Moreover, in each of the above-described
embodiments and modifications, some or all of the functions and
processes implemented by software may be implemented by hardware.
Also, some or all of the functions and processes implemented by
hardware may be implemented by software. Various types of circuits,
such as an integrated circuit, a discrete circuit, or a circuit
module that is a combination of these circuits may be used as
hardware.
* * * * *